1. Field of the Invention
The present invention relates to a resonator and a dielectric filter.
2. Description of the Related Art
As a communication system using a high-frequency radio wave in a microwave-band or a millimeter-wave band as a carrier, for example, a telephone system such as a cellular phone or a wireless local area network (LAN) has become widely used, it has become possible to transmit and receive a variety of types of data easily and not through a repeater etc., at a variety of places both indoors and outdoors.
An instrument used in such a communication system is provided with a filter element such as a low-pass filter (LPF), a high-pass filter (HPF), or band-pass filter (BPF). The filter element is designed so that it can be used in a distributed parameter circuit, not in a lumped parameter circuit, in order to process a signal in the high-frequency band. For example, a filter having a tri-plate structure is formed using a pair of parallel electric conductor patterns.
Further, to carry the instrument easily, an attempt has been made to miniaturize it by means of high-density packaging, multi-layering of its substrates, etc. For example, in configuring of pattern wiring line layers, dielectric insulating layers, etc. into a multi-layered structure, such layers in which filters, capacitors, inductors, registers, etc. are formed and pattern layers in which signal wiring lines, power supply lines, etc. are formed are configured into a multi-layer structure to provide a high-frequency module device in practice.
However, in the case of, for example, a comb-line type filter by which one pair of conductor patterns each having a length that is one fourth a wavelength of a signal to be transmitted therethrough is coupled to each other electromagnetically, if the signal to be transmitted has a low frequency, the conductor patterns must be elongated, to make it impossible to miniaturize the filter.
Furthermore, if an instrument is miniaturized by configuring into a multi-layer structure such layers as filter layers designed as those of a distributed parameter circuit and pattern wiring line layers, behaviors of the filter are influenced by signal wiring line patterns etc, thus making it impossible to obtain desired filter characteristics in some cases. For example, if a signal wiring line pattern is arranged between a grounding conductor layer and conductor patterns, a condition of electromagnetic coupling between one pair of parallel conductor patterns changes, thereby making it impossible to obtain desired filter characteristics in some cases.